The present invention relates to a device for sequentially loading bars into an automatic lathe.
In the known art there are automatic lathes which receive sequentially by means of special loaders bars from which to make pieces or machined sections. The loader inserts axially the end of a bar behind the lathe chuck. The chuck comprises a clamp which grasps the bar and moves it axially beneath the machining tools for a length predetermined to be the actual length of the work to be machined. After completion of machining of the workpiece it is cut off and the clamp withdraws by running along the bar to return to the starting position, grasp the bar again and again advance to feed beneath the tools the section to be machined. The sequence of operations is repeated until the bar is exhausted. At this point the loader withdraws the remaining bar stub, discards it and inserts a new bar in the lathe so that the machining cycle can resume automatically.
There being inserted in the lathe only a short section of bar at a time, for the entire cycle of machining the bar is supported at the rear by the loader in such a manner that the bar can rotate in the chuck without bending or vibration. In addition, the rear end of the bar must remain constrained to the loader so that the final stub to be discarded can be withdrawn.
For the productivity of the machining station consisting of the combination of loader and lathe, it is essential that all the operations follow at high speed. In the embodiments of the known art a problem is synchronised operation of the loader and lathes especially during feeding of the sections to be machined and return of the clamp to the starting position.
Indeed, the bar must remain constrained at the rear to a loader clamp which is moved by a kinematic device, usually a chain, so as to push the bar into the lathe and subsequently withdraw the stub to be discarded. But during machining the bar must be moved with precision by the lathe clamp which thus moves not only the bar but must overcome the friction of the mechanism (in the meantime placed in idle) for movement of the loader clamp.
In addition to being difficult due to the effort required and for possible positioning errors it is also dangerous due to the possibility that the bar tail could slide out of the loader clamp, where it is usually held merely by elastic grip, during forward acceleration of the lathe clamp. Furthermore, during rearward travel of the lathe clamp the bar pushes the loader clamp handling mechanism. This could cause bending of the rotating bar with resulting strong vibrations.